English Reference
Idiom idiom

modus operandi

C1 Roman origin
Meaning

A person's characteristic way of doing something, recognisable across occasions.

Examples
SIMPLE

“Flattery first, then the request — that's his modus operandi.”

CONTEXTUAL

“The two burglaries shared a modus operandi precise enough to link them in a single file.”

COMPLEX

“The firm's modus operandi was consistent across a decade of acquisitions: buy quietly, keep the founders on for eighteen months, and rename everything the week after they leave.”

Origin

Modus operandi is Latin for mode of operating, and the vocabulary is Roman — modus, a measure or manner, is one of the most heavily used nouns in Roman legal and philosophical writing.

The phrase itself is a later Latin construction that English picked up in the seventeenth century for any settled method of working. Its modern career belongs to police work: as criminal investigation became systematic in the nineteenth century, detectives began filing offences by the way they were committed, on the assumption that the method is more consistent than the disguise. Officers abbreviated it to MO, and crime writers spread the abbreviation everywhere.

In general English the phrase has kept the detective's implication. Describing someone's modus operandi suggests a pattern observed from outside, and often one they would rather not have had noticed.

The Law's Latinconnected storiesSee all Roman origin →

Roman legal Latin that never left the courtroom — or the boardroom.

  1. 01

    bona fide (idiom)

    Genuine and honestly meant — the real thing, not a pretence.

    The Roman standard of good faith.
  2. 02

    caveat emptor (idiom)

    Let the buyer beware — checking what you are buying is your own problem.

    What Rome did not actually say.
  3. 03

    quid pro quo (idiom)

    Something given in return for something else, usually as an understood trade.

    From the apothecary's substitute.
  4. 04

    de facto (idiom)

    In practice, whatever the official position says.

    The question of fact.
  5. 05

    de jure (idiom)

    According to the law, whether or not that is what actually happens.

    The question of law.
  6. 06

    ipso facto (idiom)

    By that very fact — the consequence follows automatically, with no further step.

    Consequences that need no hearing.

Last updated August 3, 2026